1. Related Applications
This application is related to several other patent applications which are commonly owned by the Assignee of this application. Those related applications are: U.S. Design patent application, Ser. No. 29/081,929 entitled Computer Cabinet, U.S. patent application, Ser. No. 08/970,503 entitled Cooling System for Semiconductor Die Carrier, U.S. patent application, Ser. No. 08/970,379 entitled Multi-Chip Module, and U.S. patent application, Ser. No. 08/970,434 entitled Decorative Panel for Computer Enclosure, all of which are hereby incorporated by reference.
2. Field of the Invention
The present invention relates to a computer system, and more particularly, to a computer system architecture.
3. Description of the Related Art
Conventional computer systems contain electronic components that are located on printed circuit boards (PCBs). PCBs are also called "cards," "daughtercards," or "motherboards." Conventional computers contain the majority of their components on a main PCB called a "motherboard." The motherboard usually contains at least a processor, memory, and a peripheral controller. The motherboard usually also contains various bus logic chips, buffers, bus protocol circuitry, and memory management chips.
Some conventional systems include PCBs in addition to the motherboard. These additional PCBs typically plug into sockets in the motherboard (also known as expansion slots) and PCBs contain electronics used by the motherboard, where the electronics are of a type compatible with the motherboard. Such electronics may include controllers for add-on peripherals, video circuitry, sound circuitry, etc. Other conventional systems contain a memory subsystem in low-bandwidth pluggable modules (called single in-line memory modules or "SIMMs") on one or more separate PCBs.
The electronic elements on a motherboard are connected to one another on the motherboard by one or more "busses" and by lines carrying various control signals. Busses transmit addresses, data, control signals, etc. between electronic components. A motherboard is connected to other PCBs by one or more "connectors." Each connector has "pins," some of which transmit signals that are passed between the motherboard and the other PCBs and some of which are connected to power or ground. Signal paths called "traces" connect the connectors on the PCBs, backplanes, and/or motherboards.
Conventional connectors that are used to connect PCBs cannot achieve a density much higher than eighty contacts per linear inch. This low density limits the number of pins that can be located on a connector and limits the possible width of busses connecting the motherboard to other PCBs. In addition, when a connector contains a relatively small number of pins, signals are often multiplexed on at least some of the pins. When two signals are multiplexed on a single pin, for example, the signals are transmitted at different times over the single pin.
Multiplexed signals add electronic overhead and slow the operational speed of the system. As an alternative to narrow busses and multiplexed signals, some conventional systems simply use very large connectors. Such a size increase causes timing problems. Similarly, undesirable effects such as noise, signal disturbances, propagation delay, and cross-talk increase along with connector size. Some connector pins must be used for power and ground signals. It is desirable to have a relationship of 2:1 or 3:1 between signal and power/ground. Yet, such a relationship is not possible within the limitations of conventional low density connectors. Thus, the pin-out limits and size of conventional connector technology places limitations on the types of electronic components that can be located on boards other than the motherboard.
Generally, conventional computer systems include a processor on the motherboard. Some conventional systems allow a user to substitute processors by unplugging a first type of processor chip from the motherboard and replacing it with a second type of processor chip. Such substitution, however, can only be performed between processor chips having identical bus sizes and similar architectures. Specifically, both processor chips must be compatible with the other electronics on the motherboard.
The evolution of the personal computer has been marked by significant increases in processor speed. Bus widths have continued to increase for every new generation of processor. It is now common to integrate memory management and peripheral support functions into "chip sets." The introduction of a new processor or chip set has previously required that the computer's motherboard be redesigned to benefit fully from the increased functionality and bandwidth of the new processor. The high speeds and dense packages dictate that the processor, the chip set, and the bus that interconnects them be placed on a single motherboard. The use of a motherboard limits the extent to which an existing system can be upgraded when new technologies become available because a motherboard is designed to operate only with certain bus widths, memory management schemes, peripheral busses and expansion slots.
In general, therefore, it is desirable to make the components of a computer system as modular as possible. When most of the components of a computer system are located on a motherboard, the motherboard will necessarily be large. Manufacture of these large boards is more complex than manufacture of small boards and, therefore, large boards are more difficult and costly to manufacture. In general, the effects of the many small tolerances required by a large motherboard combine to cause manufacturing problems for large boards, resulting in a lower yield of usable boards during the manufacturing process. Large boards also must be thicker than small boards to avoid warpage and to facilitate routing of tracer.
In addition, the larger a board is, the more components are located on the board. Large boards are also more difficult and costly to repair than small boards because, for example, if a single component on a motherboard is faulty, the entire board must be removed from the computer for repair or replacement. As stated above, although it is desirable to have modular components in a computer system, the pin-out limits of conventional connectors make modularity impractical.
In a co-pending U.S. patent application Ser. No. 09/083,083 filed on May 22, 1998, entitled Passive Backplane Capable of Being Configured to a Variable Data Path Width Corresponding to a Data Size of the Pluggable CPU Board the Applicants have disclosed a passive backplane computer architecture which includes a pluggable central processing unit card including a microprocessor, a pluggable memory circuit card, a pluggable bridge circuit card, and a plurality of connectors or card slots in the passive backplane. The signal routing between these connectors on the backplane are designed to maximize the number of uncommitted or undefined signals between various card slots to allow flexibility in designing the cards. For example, of the 18 connectors disclosed in the preferred embodiment, signals from five of the connectors are predefined between various card slots whereas signals for the remaining thirteen connectors are not predefined to provide a flexible architecture.
Operation speed continues to be one of the main selling points for computers and other data processing equipment. Increases in operation speed lead to expanded capabilities in graphics, communications, and database applications, to name just a few. One way of increasing the operation speed of an electronic system is to reduce the board area by locating the components of the computer system closer together to reduce the wiring path or traces between the components. Propagation delay increases as the length of the traces between the components increases. Moreover, configurations with a high concentration of components within a small board area are difficult to cool. This is significant because the temperature at which a component, such as the microprocessor, is operated affects its operation speed. In general, a cool component may be reliably operated at higher speeds than a hot component. Modern high speed components have demanding cooling requirements, and future designs are likely to be even more demanding. Accordingly, the abilities to reduce the tracing paths between components and to cool the components are important factors in obtaining reliable, high speed operations of electronic systems.
As computers become smaller and as greater numbers of components are integrated within the casing of computers, the internal structure and layout becomes problematical. It is desirable to make computers having a small size. Yet, at the same time, as more components are added, servicing and upgrading become more difficult, while the cooling requirements of the computer may increase.
In conventional computers, the printed circuit boards that contain a CPU and its related electronics, as well as memories, and peripheral devices, such as hard disk drives and floppy disk drives, are housed in a single enclosure, devoid of internal partitions. All the elements that make up the computer reside in a single open area within the casing of the computer, containing only brackets necessary to support the components. There is generally no structure in these conventional arrangements to effectively separate the internal elements from one another to prevent heat and electromagnetic radiation generated by the components from considerably affecting the other elements within the enclosure.
Accordingly, there exists a need in the art to provide, among other things, an economical interface optimized computer architecture that is designed to allow for optimized trace distances between components, be compatible with high speed internal components, facilitate cooling and be designed so that its various components are easily accessible during upgrade and/or repair.